1. Field of the Invention
The present invention relates to a starter for starting an internal combustion engine, the starter being equipped with a planetary gear reduction mechanism, as well as to the method of manufacturing the starter.
2. Related Art
In a conventional starter equipped with a planetary gear reduction mechanism, as disclosed in Japanese Utility Model Application Laid Open S59-121474, Japanese Utility Model Application Laid Open H1-69183, Japanese Utility Model Application Laid Open H4-32268, and Journal of Nippondenso Technical Disclosure 72-055, holes adapted for the insertion of the planetary gear shaft are bored in a planetary gear shaft supporting member, which is pre-manufactured integral with a drive shaft. The planetary gear shaft including a pin, i.e., a roller, and other elements is inserted in the holes in the supporting member by press-fitting or other methods.
According to such a method as associated with conventional starters having planetary gear reduction mechanism, however, as disclosed by Utility Model Laid Open H4-32268, it was necessary to increase the thickness of the planetary gear shaft supporting member in order to reinforce the bonding strength between the planetary gear shaft and the planetary gear shaft supporting member.
When the thickness of the planetary gear shaft supporting members is increased, the diameter of the planetary gear shaft supporting member is likewise increased, as is the inertial mass of the drive shaft. As a result of the increase in the size of the supporting member, the number of impacts at repeated engagements of a rotating pinion gear is also increased and teeth of both the pinion gear and a ring gear of an internal combustion engine may be broken, thus requiring increased maintenance.
Instead of increasing the thickness of the planetary gear shaft supporting member as described above, it has also been proposed that the bonding strength may be reinforced by heat treatment of the planetary gear shaft supporting member. However, despite such attempts, it is still necessary to considerably thicken the planetary gear supporting member.
Moreover, in order to integrate the drive shaft and the planetary gear shaft supporting member, hereinafter simply called "the supporting member", although the supporting member is formed conventionally by pressing and extending the drive shaft in a forging process, the problem existed that the forging process was complicated as it required a multiple number of forging steps and complications arose in that the diameter of supporting members was notably larger than that of the drive shaft.
The process is further complicated because, when press-fitting the planetary gear shafts into the supporting member, it is necessary to bore holes for a plurality, e.g., three pieces, of planetary gear shafts on the supporting member, to remove burrs and to press-fit these shafts.